1. Field of the Invention
The present invention relates to pilot control relay valves having means for recovering exhaust fluids, particularly gasses. Even more particularly, the present invention relates to a pilot control relay valve employed not only to change the directional flow of fluids to a piston, valve or the like wherein controls provide a fluid signal to drive an end device, such as a chemical injection pump to inject chemicals at a slow or rapid rate over a long period of time, but to recover exhaust gases without the adverse effects of back pressure.
2. General Background
Various devices are known which attempt to control a reciprocating pump. Devices of one such type are used in attempting to control a glycol pump which controls the level of liquid in a gas-liquid system and for circulating liquid in a gas-liquid system. These devices require a separate pump and pilot assembly such as that illustrated in U.S. Pat. No. 2,990,910 entitled "Apparatus And Method For Circulating Controlling Liquids In Gas-Liquid Systems" issued to G. 0. Kimmell. Most pertinent, however, is U.S. Pat. No. 4,776,773 entitled "Pilot Control Valve For Controlling The Pumping Rate of An Injection Pump" issued to A. J. Quartana, III. However, Mr. Quartana's teaching contemplates aspiration of the control fluid to atmosphere (ambient) pressures, even more particularly to outside air. As such, Mr. Quartana's teaching is structurally incapable of recovering any exhaust fluids even though it relieves pressure on the output or "low" side and increases pressure on the input or "high" side, thereby allowing the pump to reach a low speed or pumping rate. Exhaust fluid recovery is highly significant and desirable when the control fluid used is environmentally hazardous or a pollutant gas, as is the case with natural gas and "sour" (H.sub.2 S impregnated) gas among others. Such usage is commonplace in many parts of the world where natural gas exists under pressure and offers a ready source of motive energy. Further usefulness of gas recovery can be seen in applications where a gas-driven device is housed indoors and the user would wish to prevent gas buildup and possible explosion hazard.